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Search: id:A005561
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| A005561 |
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Number of walks on square lattice.
(Formerly M3596)
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+0
3
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| 1, 4, 24, 84, 392, 1344, 5760, 19800, 81675, 283140, 1145144, 4008004, 16032016, 56632576, 225059328, 801773856, 3173688180, 11392726800, 44986664800
(list; graph; listen)
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OFFSET
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3,2
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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R. K. Guy, Catwalks, Sandsteps and Pascal Pyramids, J. Integer Seqs., Vol. 3 (2000), #00.1.6
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FORMULA
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a(n) = C(n+4, ceil(n/2))*C(n+3, floor(n/2)) - C(n+4, ceil((n-1)/2))*C(n+3, floor((n-1)/2)). - Paul D. Hanna (pauldhanna(AT)juno.com), Apr 16 2004
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PROGRAM
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(PARI) {a(n)=binomial(n+4, ceil(n/2))*binomial(n+3, floor(n/2)) - binomial(n+4, ceil((n-1)/2))*binomial(n+3, floor((n-1)/2))}
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CROSSREFS
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Cf. A005558-A005562, A093768.
Sequence in context: A112742 A158494 A069145 this_sequence A061612 A097875 A026694
Adjacent sequences: A005558 A005559 A005560 this_sequence A005562 A005563 A005564
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KEYWORD
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nonn,walk
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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